import java.util.Arrays;
import java.util.EmptyStackException;

public class MyStack {
     public int[] elem;
     public int usedSize;

    public MyStack() {
       this.elem = new int[10];
    }
    public void push(int val){
        if(isFull()){
            this.elem = Arrays.copyOf(elem,2*elem.length);
        }
        elem[usedSize++] = val;
//        elem[usedSize] = val;
//        usedSize++;
    }
    public boolean isFull() {
        return usedSize==elem.length;
    }
    public int pop(){
        if(isEmpty()){
            throw new EmptyStackException();
        }
        int val = elem[usedSize-1];
        usedSize--;
        return val;
    }
    public int peek(){
        if(isEmpty()){
            throw new EmptyStackException();
        }
        int val = elem[usedSize-1];
        return val;
    }
    public boolean isEmpty(){
        return usedSize==0;
    }
}
